One example of a laser printer well known in the art is a tandem-type color laser printer having four photosensitive drums arranged in tandem and parallel to one another. The photosensitive drums are provided respectively for the colors yellow, magenta, cyan, and black.
Surrounding each of the photosensitive drums is a corresponding Scorotron charger, a developing roller, a transfer roller, and the like.
During an image-forming operation, each charger charges the surface of the corresponding photosensitive drum with a positive polarity through corona discharge while the photosensitive drum rotates. The charged surface of the photosensitive drum is then selectively exposed to a laser beam that eliminates the charge in the exposed areas, forming an electrostatic latent image on the surface of the photosensitive drum.
As the photosensitive drum continues to rotate, bringing the electrostatic latent image into confrontation with the developing roller, the developing roller supplies toner to the electrostatic latent image. The toner develops the latent image into a toner image. Thus, a toner image is now carried on the surface of the photosensitive drum.
As the photosensitive drum continues to rotate, bringing the toner image to a position opposite the corresponding transfer roller, a sheet of paper is conveyed to the contact area between the photosensitive drum and transfer roller in synchronization with the timing of the rotating toner image. The toner image is transferred from the surface of the photosensitive drum onto the sheet of paper passing between the photosensitive drum and transfer roller, forming an image on the paper.